1. Field of the Invention
The present invention is related to fluid impermeable seals, and specifically to an apparatus and method for creating such seals in a centrifugal blood pump after sterilization thereof.
2. Description of the Prior Art
Centrifugal pumps have been used for many years to pump a wide variety of different fluid materials. In general, a centrifugal pump includes a pumping chamber with an inlet aligned with a rotational axis of the pump, an outlet adjacent the periphery of the pumping chamber, and an impeller mounted within the pumping chamber for rotation about the axis. The impeller in such pumps can be mounted on a drive shaft which extends outside the pumping chamber to a rotational drive source or the shaft can be mounted within the pumping chamber as a spindle about which the impeller rotates (rotatably driven by means other than the rotation of the shaft, such as a magnetic drive arrangement). In any case, as the impeller is rotated, it imparts centrifugal force and velocity to the fluid, thus pumping the fluid from the pump inlet to the pump outlet.
In recent years, centrifugal pumps have been used extensively for pumping blood during open heart surgery. Examples of centrifugal blood pumps are shown in the following U.S. Pat. Nos.: Rafferty et al Re. 28,742; Dorman et al 3,608,088; Rafferty et al 3,647,324; Kletschka et al 3,864,055; Rafferty et al 3,957,389; Rafferty et al 3,970,408; Rafferty et al 4,037,984; and Reich et al 4,135,253.
The pumping of blood requires great care to avoid any damage to the red corpuscles, or any of the other constituents of blood. Any practical blood pump useful as part of heart/lung bypass equipment during open heart surgery must deliver the requisite flow volumes under pressure, without damaging the blood being pumped.
In a centrifugal pump, and in particular in a centrifugal pump for pumping liquids such as blood, a fluid tight seal between the drive shaft and the housing is an important factor in terms of both performance of the pump and non-contamination of the blood being pumped. If the seal is not complete (i.e., permeable), lubricants for the rotating parts of the pump or other contaminants might seep into the blood, or vice versa, which are undesirable situations for a number of reasons, including medically-related concerns and potentially decreased pump life.
Disposable blood pumps, because of their use in surgery, must be supplied sterile and ready for use. Typically, the most common method of sterilizing such a pump is for the unit to be sealed in a gas permeable bag and then exposed to ethylene oxide gas (ETO). Prior art disposable centrifugal blood pumps generally have two separate chambers--a chamber which will contain the blood being pumped and a chamber which contains the bearings for the rotating portions of the centrifugal blood pump. Blood is excluded from the bearing chamber by a shaft seal. Although the bearing chamber should never have blood contact, it must be sterilized to avoid the possibility of contamination due to a seal leak.
Prior art centifugal blood pumps have been made with a lip seal between the pumping and bearing chambers and were assembled with a short length of nylon monofilament line between the lip seal and the shaft before the blood pump assembly is sealed in its gas permeable bag. Thus, when the pump is exposed to ethylene oxide gas, the gas can enter and sterilize the bearing chamber through the gap caused in the seal by the presence of the nylon line. One end of the nylon line extends out the outlet of the blood chamber so that it can be grasped through the sterile bag and pulled out of the pump (after ETO exposure) before the pump is boxed for shipment. Of course, each bag then contains not only a sterile pump, but a short length of nylon line.
There are two principal disadvantages to the above described method of pump sterilization. First, extra packaging and handling is required. Second, the nylon bearing chamber line sterilization method precludes prepackaging of centrifugal blood pumps in sterile tubing packs preferred for use by perfusionists in their heart lung consoles. The pre-packaging of such devices such as filters into a pre-connected set-up before sterilization is now in common use because of its convenience and because it minimizes the danger of contamination by bacteria.
In some prior art centrifugal blood pumps, the bearing chamber has a separate inlet in its housing for introduction of fluid lubricant and later the introduction of ETO gas during sterilization. Of course, this arrangement presents the added complexity of requiring this inlet to be sealed after sterilization and the use of fluid bearings increases the cost of such blood pumps. If the bearing chamber were left unsealed, a patient could be exposed to a potentially fatal infusion of air into the blood stream should the seal between the blood pumping chamber and the bearing chamber fail during use.